A COMET knocked from the fringes of the solar system one million years ago and discovered by a Scottish astronomer only last year is set for an epic “near miss” with Mars this weekend.
Comet Siding Spring will hurtle within 87,000 miles of the red planet – considered a close shave in space terms – providing an unprecedented opportunity for scientific imaging and analysis by a waiting fleet of spacecraft.
“This is an absolutely spectacular event,” said Jim Green, director of Nasa’s planetary science division.
“We are going to observe an event that happens maybe once every million years, where a comet coming from the furthest reaches of the sun’s gravity will come to the inner part of our solar system.”
The so-called “dirty snowball” of ice, dust and frozen gases, is a 4.6 billion-year-old remnant from the formation of the solar system and used to inhabit the Oort Cloud, a vast area of space on the outer fringes of our solar system, until an interaction with a passing star sent it on a route towards the inner system.
It was first detected in January last year by Robert McNaught, a Scottish-born astronomer at the Australian National University in Canberra, known as the “world’s greatest comet discoverer”. He has found 82 of them.
Siding Spring, named after the Australian observatory from which it was first seen, will streak past Mars at 126,000mph. Its tail of dust is so vast, measuring 300,000 miles in length, that it will engulf the whole of Mars as it passes.
The comet will be met by a “welcome party” of five orbiting spacecraft operated by the US space agency, Nasa, and by the European and Indian space agencies, that will image and analyse its composition and interaction with the Martian atmosphere.
They have all been moved into a “duck and cover” position behind the planet to protect them from the debris spewing from the comet’s nucleus at 60km per second.
Curiosity and Opportunity, Nasa’s two rovers working on the surface of Mars, will also shift their camera gaze skywards to witness the fly-by and what could be a glittering meteor shower over the red planet.
The fleet will provide scientists with unprecedented close-up observations of a comet.
“We have fingers crossed for the first images of a comet from the surface of another world,” said Kelly Fast, a scientist in Nasa’s planetary science division.
“Normally, we would send spacecraft to a comet. In this case, the comet is coming to the spacecraft.”
Because Siding Spring has never entered the inner solar system before, it has not been altered by prior interaction with the sun, giving it added scientific value.
“Its material is virtually unchanged by the rays of the sun and can give us an insight to the material composition of our early solar system 4.6 billion years ago,” explained Dan Brown, an astronomy expert at Nottingham Trent University.
“The Mars fly-by is exciting since we have so many different instruments on so many different spacecrafts working together. Not one of these was initially designed for such a project, yet the science teams behind them were able to adapt and set up observations that should give us a view of comets, the matter they are made out of and ultimately what made our solar system.”
From the surface of Mars, the comet – which will make its closest approach to the planet at 7:28pm UK time tomorrow night – will appear overhead three times brighter than Venus appears from Earth.
From earth, however, the comet will not be visible to the naked eye, though skywatchers in the UK with moderate-sized telescopes may be able to spot it around an hour before its closest approach, seven degrees above the horizon.